For delineating a pattern of a semiconductor integrated circuit on a resist material formed on a substrate formed by, for example, a silicon semiconductor substrate, an electron ray beam used for delineation is transmitted through the resist material to fall on the substrate. The electron ray is scattered in a broad range within the substrate. That is, the so-called backward scattering in electron ray lithography is produced. Part of the electron ray beams agin falls on the resist material. The result is that the resist material is sensitized over a range significantly wider than an area on which the electron ray beam has entered the resist material. If the delineation pattern is low in density, the light exposure of the resist material ascribable to backward scattering is negligible. However, if the delineation patterns are congested and lie close to one another, light exposure of the resist material ascribable to backward scattering occurs over an extremely wide range. This phenomenon, schematically shown in FIGS. 26A and 26B, is the proximity effect in the electron ray lithography. Up to now, various methods for correcting the proximity effect have been proposed.
The conventional method for correcting the proximity effect and the problems thereof will now be briefly explained.
Before proceeding to description of the method for correcting the proximity effect including that of the present invention using various equations, the variables used therein are first defined. The unitary domain is synonymous with mesh. A delineated figure is synonymous with a pattern to be delineated in the unitary domain, and means a pattern to be delineated using an electron ray beam present in the unitary domain. A pattern density A% means the percentage of the sum total of sub-areas occupied by patterns in the entire area. Meanwhile, a suffix `v` to a symbol `.DELTA.` means a vector.
.eta.: backward scattering coefficient in an EID function (also termed a reflection coefficient) PA1 .beta..sub.f : radius of forward scattering in the EID function PA1 .beta..sub.b : radius of backward scattering in the EID function PA1 W: length of a side of a rectangular-shaped delineated figure or length of a side of a square-shaped delineated figure PA1 eb(x, y): accumulated energy, ascribable to backward scattering, exerted by a delineated figure on a point (x, y) PA1 eb.sub.p, q (x, y): accumulated energy, ascribable to backward scattering, exerted by a delineated figure positioned at a unitary domain (p, q) on a point (x, y) PA1 Eb(x, y): accumulated energy, ascribable to backward scattering, exerted by all delineated figures on a point (x, y) PA1 Eb(i, j): accumulated energy, ascribable to backward scattering, exerted by all delineated figures on a unitary domain (i, j) PA1 .DELTA..sub.v Eb(i, j): gradient vector of accumulated energy, ascribable to backward scattering, exerted by all delineated figures on a unitary domain (i, j) PA1 .DELTA..sub.v EB.sub.x,i,j : x-axis component of a gradient vector of accumulated energy, ascribable to backward scattering, exerted by all delineated figures on a unitary domain (i, j) PA1 .DELTA..sub.v EB.sub.y--i,j : y-axis component of a gradient vector of accumulated energy, ascribable to backward scattering, exerted by all delineated figures on a unitary domain (i, j) PA1 .alpha..sub.x--i,j : x-axis component in a pattern area density in a unitary domain (i, j) PA1 .alpha..sub.y--i,j : y-axis component in a pattern area density in a unitary domain (i, j) PA1 .alpha.'(i, j): an averaged pattern area density in a unitary domain (i, j) PA1 .DELTA..sub.v .alpha.(i, j): gradient vector of an averaged pattern area density in a unitary domain (i, j) PA1 .DELTA..sub.v .alpha..sub.x--i,j : x-axis component of gradient vector of an averaged pattern area density in a unitary domain (i, j) PA1 .DELTA..sub.v .alpha..sub.y--i,j : y-axis component of gradient vector of an averaged pattern area density in a unitary domain (i, j) PA1 S.sub.th : threshold value of gradient vector of pattern area density (pre-set value) PA1 R.sub.sm : averaging range (number of unitary domains used for averaging) PA1 N.sub.sm : number of times of averaging PA1 D: exposure dose PA1 D.sub.s : standard exposure dose giving a target size of a delineated pattern in a pre-set pattern density (such as 50%) PA1 D.sub.cor (i, j): corrected exposure dose in a unitary domain (i, j) PA1 D.sub.cor (x, y): corrected exposure dose at a point (x, y) PA1 .DELTA.L.sub.mesh : variation in line width in a unitary domain PA1 .DELTA.L: variation in line width for variation in light exposure dose (.DELTA.Eb/Ds) at a pre-set pattern density, such as 50% (in other words, line width variation in a unitary domain) PA1 .DELTA.L.sub.tol : tolerance of line width variation in a unitary domain PA1 L.sub.x, L.sub.y : size of divided pattern in the x-axis direction and in the y-axis direction PA1 Eb.sub.-- EIB.sub.n (i,j): accumulated energy (based on EID function) of accumulated energy ascribable to backward scattering at the center of a unitary domain (i, j) after N times of iterative calculations PA1 Derr.sub.-N (i, j): error in exposure dose at the center of the unitary domain (i, j) after N times of iterative calculations PA1 .alpha."err.sub.-N (i, j): difference between corrected pattern area density after N times of iterative calculations and pattern area density estimated from accumulated energy ascribable to backward scattering derived from the EID function PA1 Eb.sub.-g (i, j): accumulated energy ascribable to backward scattering at an areal center of gravity in a pattern in a unitary domain (i, j) (total delineated figure) PA1 Ddiv.sub.-- cor(x.sub.div--c, y.sub.div--c): corrected exposure dose of an electron ray beam at the center of a divided pattern (x.sub.div--c, y.sub.div--c) PA1 .eta. is the backward scattering coefficient; PA1 .vertline..DELTA..sub.v .alpha..sub.x--i, j ".vertline. is the magnitude of an x-axis component of a gradient vector of a pattern areal density obtained based on the corrected pattern areal density obtained by last repetition of the step of calculating the accumulated energy obtained based on the pattern areal density corrected in the unitary domain where the magnitude of the gradient vector exceeds a pre-set value; PA1 .vertline..DELTA..sub.v .alpha..sub.y--i, j ".vertline. is the magnitude of a y-axis component of a gradient vector of a pattern areal density obtained based on the corrected pattern areal density obtained by last repetition of the step of calculating the accumulated energy obtained based on the pattern areal density corrected in the unitary domain where the magnitude of the gradient vector exceeds a pre-set value, PA1 D.sub.s is a standard exposure dose affording a target size of a pattern for delineation in a pre-set pattern density and PA1 Eb.sub.--g (i, j) is an accumulated energy ascribable to backward scattering at an areal center of gravity (X.sub.--g, Y.sub.--g) of a pattern in a unitary domain where the magnitude of the gradient vector is not less than a pre-set value.
(Method for Sequential Calculations by Representative Point Evaluation)
The method for sequential calculations by representative point evaluation, widely employed as a method for correcting the proximity effect, is a exposure dose optimizing method consisting in providing representative points at each corner and at a central point in each side of a figure for delineation and calculating the intensity of light exposure at each representative point using an energy intensity distribution (EID) function for optimizing the exposure dose in each light exposure shot into coincidence with the threshold value of the exposure light energy required for forming a resist pattern. This method is explained in, for example, M. Parikh, J. Appl. Phys, 50 (1979), 4371 or M. Parikh, J. Appl. Phys, 50 (1979), 4378 or M. Parikh, J. Appl. Phys, 50 (1979), 4383.
The calculations for correction can be divided into calculations of the accumulated energy at a representative point P(x, y) for a given figure for delineation and calculations for optimizing the exposure dose. In the calculations for the accumulated energy at the representative point P(x, y) in a given figure for delineation, an accumulated energy Q(x, y) ascribable to backward scattering, brought about by other figures, is calculated using the following equation (1): ##EQU1##
The range of a proximate figure affecting a representative point P(x, y) is at least thrice a backward scattering radius (.beta..sub.b) defined by the EID function of the following equation (2): ##EQU2## as proposed by T. H. P. Chang, J. Vac. Soi. Technol. 12, 1271 (1983). The range equal to three times the radius of backward scattering (.beta..sub.b) is schematically shown in FIG. 27 by a solid-line circle. The term of D(x', y') on the equation (1) represents a light exposure image (pattern).
Then, the sum of squares of the differences between the accumulated energy Q(x, y) at each representative point P(x, y), as calculated using the equation (1), and the prescribed intensity of the exposure light at each representative point (in most cases, the exposure dose at an edge E.sub.th) is found for quantitating the magnitude of the proximity effect. The exposure dose at each light exposure shot is adjusted, that is corrected, and the sum total of the squares of the differences is re-evaluated. The exposure dose at each light exposure shot is adjusted, that is corrected, for minimizing the sum total of the squares of the differences.
In keeping with the smaller feature size and higher integration of a semiconductor integrated circuit, the number of figures to be delineated per chip for pattern delineation by an electron ray beam, is increasing drastically. On the other hand, in keeping with the tendency towards development of high resolution electron ray lithography is towards higher acceleration voltage for an electron ray beam, a light exposure device of 30 kV or 50 kV has made its debut. Further, a light exposure device of 100 kV is about to make its debut. If the acceleration voltage is 20 kV, the radius of backward scattering .beta..sub.b is 3 to 5 .mu.m, whereas, if the acceleration voltage is 50 kV, the radius of backward scattering .beta..sub.b is on the order of 10 .mu.m. With increased acceleration voltage, the radius of backward scattering .beta..sub.b is increased significantly, as shown by a broken-line circle, such that, with increased number of figures for delineation, the processing time required for calculations for correction in the sequential computing method by the conventional representative point evaluation is prohibitively increased beyond practically tolerable level.
The correction for the proximity effect by the sequential calculating method in square-shaped figures for delineation with each side measuring W .mu.m, arrayed at an interval of W .mu.m (see FIGS. 27 and 28). FIG. 28 shows only one of the figures for delineation. These figures may be deemed to be of patterns with a design rule of W .mu.m. The accumulated energy ebp,q (x, y) ascribable to backward scattering, exerted by a figure lying at a unitary domain (p, q) on a point P(x, y), is first found by the following equation (3) ##EQU3##
In the equation (3), (X, Y) is a coordinate of a center point of a square-shaped figure of a length of a side W lying at the unitary domain (p, q). As figures affecting the point P(x, y), at least the figures situated in a range thrice the radius of backward scattering .beta..sub.b need to be considered. If the sum of the influences of the accumulated energy from these figures is taken into account, the accumulated energy Ebi, j(x, y), ascribable to backward scattering in the unitary domain (i, j) can be found from the following equation (4): ##EQU4##
In keeping pace with the tendency towards smaller feature size of the design rule (W), the number of figures per unit area is evidently increased, so that the processing volume for calculating the accumulated energy by the sequential calculation method by the conventional representative point evaluation is increasing.
For achieving smaller feature size of the design rule (W), it is necessary to increase the resolution of electron ray delineation, for which high acceleration voltage is required. Since this increases the radius of backward scattering .beta..sub.b, the number of surrounding figures affecting the accumulated energy is drastically increased, as a result of which the processing volume for calculating the accumulated energy is also drastically increased. This is shown schematically in FIG. 29, wherein the x-axis stands for the radius of backward scattering .beta..sub.b, and the y-axis stands for the number of surrounding figures influencing the accumulated energy at the point (x, y). The respective curves denote the design rule (W). Since the number of figures of the entire chip is also increased, the total processing volume of the accumulated energy is the number of the surrounding figures influencing the accumulated energy at the point (x, y) multiplied by the total number of figures in the entire chip. Thus, the processing volume of calculations for finding the optimum exposure dose in the sequential calculation method by the representative point evaluation is prohibitive, such that, in developing the next-generation ultra-LSI, the method for sequential calculations by the representative point evaluation is not thought to be favorable.
(Representative Figure Method)
In keeping with the tendency towards the higher density and smaller feature size of the delineation pattern and higher acceleration voltage of the electron ray beam, a proximity effect correction method has been proposed, in which the calculations for correction are simplified and the time necessary for calculations for correction are drastically shortened for eking out the defect of the method for sequential calculations by the representative point evaluation in the calculation time in correcting the proximity effect. In pattern delineation using a high acceleration voltage, the range of figures exposed by backward scattering is as wide as approximately 10 .mu.m or more. It is known that, within a range of the radius of approximately 10 .mu.m, the exposure dose ascribable to backward scattering is rendered uniform based on the pattern areal density in the unitary domain, without regard to the figure. A variety of simplified high-speed proximity effect correction methods based on this feature have been proposed. One of these methods is the proximity effect correction method known as representative figure method.
With the representative figure method, shown in FIG. 30, a pattern to be delineated is divided into unitary domains (meshes) of a pre-set size. One or more figures in a unitary domain is replaced by and approximated to a rectangular figure having an area equal to the total area of the figures in the domain and positioned at an areal center of gravity and calculations for proximity effect correction are executed based on, for example, the sequential calculations by the representative point evaluation.
(Areal Density Mapping Method)
On the other hand, an areal density mapping method (also termed a bit-mapping method) consisting in developing the unitary domain (mesh) into a bit map, calculating the pattern areal density of a pattern (figure for delineation) in the unitary domain and averaging the pattern areal density of neighboring unitary domains, has been proposed and its effect has been verified. The areal density mapping method is now explained by taking a small-sized pattern (line width of 0.2 .mu.m) arranged on a boundary between a 50% pattern density area (shown on the left side of FIG. 31) and a 0% pattern density area (shown on the right side of FIG. 31) as a model pattern. Assuming that the patterning is performed on the resist material on a silicon semiconductor substrate with an acceleration voltage of 50 kV, the radius of forward scattering .beta..sub.f, the radius of backward scattering .beta..sub.b, and the reflection coefficient .eta. are set to 0.05 .mu.m, 10.0 .mu.m and to 0.78, respectively. The unitary domain is a square area delimited by a broken line in FIG. 31, with each side of the square measuring 6.4 .mu.m.
FIG. 32 shows the result of calculations of changes in pattern line width in case of not performing correction for the proximity effect. For calculating the accumulated energy, the above-mentioned EID function of the equation (2) comprised of the double Gaussian function is used. The exposure dose in an area with a pattern density of 50% was used as the standard exposure dose. Therefore, in an area with a pattern density of 50%, the pattern line width is the design line width (0.2 .mu.m). On the other hand, in an area with a pattern density of approximately 0%, the accumulated energy Eb ascribable to backward scattering is small, so that the pattern line width becomes significantly narrow. In this manner, the pattern line width is changed depending on the ambient pattern density. Moreover, with the high acceleration voltage of 50 kV, the pattern line width is significantly changed in a region of 10 .mu.m on both sides of a boundary area in which the pattern density is changed, thus inhibiting practical utilization.
The following is an example of carrying out corrections for the proximity effect by the areal density mapping method. FIG. 33 shows the flow of calculations of the areal density mapping method.
step-10!
In the areal density mapping method, delineation pattern data (EB pattern data) is read. The delineation pattern data is then split into pre-set unitary domains. Each unitary domain (mesh) is then developed into a bit map of a certain grid size. The presence or absence of the figure for delineation in each grid is described by `1` or `0`, respectively.
step-20!
Then, using this bit map, a pattern areal density per unitary domain (mesh: W .mu.m) (.alpha.(i, j) is calculated. The resulting pattern areal density .alpha.(i, j) is shown in FIG. 34.
step-30!
The calculated pattern areal density .alpha.(i, j) is averaged or smoothed. For averaging, the following equation (5): ##EQU5## is used.
That is, the operation of simple averaging of the pattern areal density in unitary domains (i+k, j+1) in the vicinity of the unitary domain under consideration (i, j) is repeated plural times. The resulting averaged areal density .alpha.'(i, j) is shown in FIG. 35. Alternatively, a weighted average value is found, on the basis of the magnitude of the effect of backward scattering on the unitary domain (i,j) under consideration, by the following equations 6-1 and 6-2: ##EQU6## where C is a constant.
By this averaging, it becomes possible to reflect the reciprocal proximity effect due to a wide range of backward scattering on the correction of the exposure dose.
step-40!
The corrected exposure dose at each unitary domain D.sub.cor (i, j) is calculated based on the averaged pattern areal density .alpha.'(i, j) (see FIG. 36). The corrected exposure dose at each unitary domain D.sub.cor (i, j) can be calculated from the following equation (7): EQU D.sub.cor (i, j)=Ds.multidot.(1+.eta.)/{1+2.alpha.'(i, j).multidot..eta.}(7)
where D.sub.cor (i, j) is a standard exposure dose and, for example, is the optimum exposure light energy in an area of 50% pattern density (such as exposure dose which gives 1:1 resolution of a large-area line and space pattern). The corrected exposure dose D.sub.cor of each rectangular-shaped light exposure shot is allocated to each unitary domain and actual pattern delineation is carried out by an electron ray beam (EB). The calculations of the pattern areal density, averaging (smoothing) and calculations of the corrected exposure dose are all arithmetic calculations which can be executed in an extremely short time.
The equation (7) is derived as follows: If the acceleration voltage of the electron ray beam is as high as 50 kV, the radius of backward scattering .beta.b is as large as approximately 10 .mu.m, such that the accumulated energy ascribable to backward scattering can be deemed to be constant. If the delineation ratio is deemed to be 100%, the accumulated energy Ef.sub.100 ascribable to forward scattering and the accumulated energy Eb.sub.100 ascribable to backward scattering for the exposure dose D can be expressed by the following equations 8-1 and 8 -2: EQU Ef.sub.100 =D/(1+.eta.) (8-1) EQU Eb.sub.100 =.eta..multidot.D/(1+.eta.) (8-2)
If the acceleration voltage of the electron ray beam is as high as 50 kV, the distribution of the accumulated energy ascribable to backward scattering is smoothed, without regard to pattern areal density, within the radius of backward scattering .beta..sub.b, such that the accumulated energy Eb ascribable to backward scattering is proportionate to the pattern areal density .alpha.(0&lt;.alpha.&lt;1). Therefore, the accumulated energy ascribable to backward scattering Eb can be found by the following equation (9): EQU Eb=.alpha..multidot.Eb.sub.100 =.alpha..multidot..eta..multidot.D/(1+.eta.) (9)
If, for a pattern areal density .alpha., the pattern edge exposure light intensity which gives the design size of a pattern is E.sub.th (.alpha.), E.sub.th (.alpha.) can be found from the following equation (10): EQU E.sub.th (.alpha.)=E.sub.th (0)+.alpha..multidot..eta..multidot.D/(1+.eta.) (10)
where E.sub.th (0) is the pattern edge exposure light intensity which gives the pattern design size for only the forward scattering (.alpha.=0). If the slicing level for E.sub.th (0), that is, for only the forward scattering, is I.sub.th (where 0&lt;I.sub.th &lt;1), the equation (10) can be rewritten to the following equation (11): ##EQU7##
If the standard pattern areal density is .alpha.s and the standard exposure dose is D.sub.cor (i, j), the equation (12), equivalent to the equation (11), may be given as: EQU E.sub.th (.alpha..sub.s)=(I.sub.th +.alpha.s.multidot..eta.)D.sub.s /(1+.eta.) (12)
Since the accumulated energy ascribable to backward scattering is varied with the pattern areal density .alpha., the pattern edge exposure light intensity is varied under the same exposure dose, as a result of which the size of a pattern formed on the resist material is changed. For avoiding this phenomenon, it suffices to correct the exposure dose D so that, under all values of the pattern areal density .alpha., the pattern edge exposure light intensity E.sub.th (.alpha.) which will give the design pattern size will become constant. That is, it suffices to set the right side of the equation (11) so as to be equal to the right side of the equation (12) and to find the corrected exposure dose D.sub.cor (.alpha.). The result is shown by the following equation (13): EQU D.sub.cor (.alpha.)=D.sub.s .multidot.(I.sub.th +.alpha..sub.s .multidot..eta.)/(I.sub.th +.alpha..multidot..eta.) (13)
If I.sub.th =0.5, .alpha..sub.s =0.5 (equivalent to light exposure with the line/space of 1:1, with the pattern density of 50%) and .alpha.'(i,j) is substituted for .alpha., the equation (7) can be derived from the equation (13). Meanwhile, it suffices if the values of I.sub.th or .alpha..sub.s are suitably set depending on the light exposure device employed or the pattern formed on the resist material, with the contents (coefficients) of the equation (7) being correspondingly changed.
An illustrative case of correction of the exposure dose in case of correcting the proximity effect by the areal density mapping method is shown in FIGS. 37 and 38 for the cases in which the length of a side of a unitary domain (W) (mesh size) is 2.56 .mu.m and no averaging has been performed, and in which the averaging range (Rsm) 3.times.3 is averaged simply with the number of times of averaging (N.sub.sm) being 9. The rectangular-shaped exposure light shot is assumed be coincident with the shape of the unitary domain. FIG. 37, showing the correction of the proximity effect by the areal density mapping method, shows changes in pattern line width in case averaging has been done and averaging has not been done, while FIG. 38 shows the corrected exposure dose D.sub.cor (x), pattern areal density .alpha.(x), averaged pattern areal density .alpha.'(x) and the accumulated energy Eb(x) ascribable to backward scattering. It is seen from FIG. 37 that, in an area with a sufficiently uniform pattern areal density (x&lt;-15 .mu.m and x&gt;15 .mu.m), the proximity effect can be corrected theoretically completely.
However, with the areal density mapping method, the accumulated energy Eb(x) ascribable to the backward scattering Eb(x) is substantially similar to the averaged pattern areal density .alpha.'(x), in a boundary area where the averaged pattern areal density .alpha.'(x), as shown in FIG. 38, such that the corrected exposure dose D.sub.cor (x), calculated based on the averaged pattern areal density .alpha.'(x), roughly reflects the reciprocal proximity effect. Therefore, in the boundary area, the proximity effect is corrected fairly satisfactorily. However, since the corrected exposure dose D.sub.cor has a stepped process with changes in the pattern areal density, it is basically not possible to avoid non-corrected remnant portions in the corrected exposure dose D.sub.cor in the unitary domain of the boundary area. The result is serrated non-corrected remnant portions in the boundary area and serrated shape of the pattern line width transitions, as shown in FIG. 37.
In addition, if the pattern density on the high density side is high, the serrated non-corrected remnant portions becomes outstanding, such that, in a pattern neighboring to an area with 100% pattern density, the non-corrected remnant portions of the corrected exposure dose D.sub.cor becomes non-negligibly high, as shown in FIG. 39. In addition, not only the pattern line width shows a serrated process in each unitary domain, but also the pattern line width is narrower than the target value, and hence the corrected exposure dose in each unitary domain on the boundary area is shifted at all times to insufficient exposure dose side, as shown in FIG. 39. Specifically, the corrected exposure dose at the center of the unitary domain (mesh) is deviated from an optimum value. In FIG. 39, `100%-0%`, `50%-0%` and `10%-0%` mean that an area with 100% pattern density and an area with 0% pattern density have been formed, an area with 50% pattern density and an area with 0% pattern density have been formed and an area with 10% pattern density and an area with 0% pattern density have been formed, respectively.
Thus, with the areal density mapping method, as one of the conventional proximity effect correcting method, residual proximity effect correction, that cannot basically be corrected, is generated in a boundary area where the pattern areal density is changed acutely, thus producing significant changes in the pattern line width. Thus, for achieving accurate proximity effect correction, it is necessary to automatically extract the unitary domains where the pattern areal density is changed acutely. In delineating a pattern, such as a pattern of a memory device, shown for example in FIG. 2, it may be supposed easily that the pattern areal density is changed acutely at a terminal portion of the cell array, such that, if the areal density mapping method is applied to this area, non-corrected remnant portions are generated therein. It is thus possible to artificially effect accurate proximity effect correction only in this area. However, in case of a complex pattern, as in the case of a logic type device or a peripheral circuit of a memory device, it is extremely difficult to artificially locate and extract a unitary domain where pattern areal density is acutely changed to give rise to uncorrected portions.
If, by a variety of proximity effect corrections, an appropriate corrected exposure dose is given each unitary domain, only a sole exposure dose can be set in each unitary domain with the conventional method for proximity effect correction. Therefore, in an area where the pattern areal density is changed acutely such that the accumulated energy Eb ascribable to backward scattering is changed acutely, uncorrected proximity effect portions in the delineated figure is basically produced. In particular, in a recent high-speed electron ray light exposure device, a variable rectangular-shaped large-diameter light beam with a diameter of 5 .mu.m at the maximum, is used for achieving a high through-put. As a matter of course, simply a sole light exposure area (light exposure shot) is given a sole rectangular beam in such light exposure device. Thus, in a large-diameter beam illuminating the boundary area, non-corrected remnant portions are inevitably produced in a beam. That is, there is imposed with the areal density mapping method a limitation on the correction accuracy in the proximity effect correction in the area subjected to acute change in the pattern areal density, although practical computing speed can thereby be achieved, such that it is difficult to effect high precision pattern delineation for the next-generation ultra-LSI with a design rule of, for example, 0.2 .mu.m or less. Therefore, in a unitary domain where the pattern areal density is acutely changed such that the accumulated energy ascribable to backward scattering is changed acutely, it is necessary to divide the pattern in a unitary domain appropriately for correcting the exposure dose in terms of the divided pattern as a unit. However, if the pattern division in a unitary domain is performed inadvertently to an extent which is more than is necessary, the data for delineation by the electron ray beam is increased in volume, which is not desirable in view of data handling and delineation time duration.